With the increased use of Computer Aided Design (CAD) solid modeling systems a new frontier of manufacturing technology has emerged that enables translation of the CAD output data into a three-dimensional (3-D) physical object. This technology is commonly referred to as solid freeform fabrication (SFF) or layer manufacturing, which entails building an object on a layer-by-layer and point-by-point basis. Forming objects automatically in three dimensions is useful in verifying CAD database, evaluating design feasibility, testing part functionality, assessing aesthetics, checking ergonomics of design, aiding in tool and fixture design, creating conceptual models and sales/marketing tools, generating patterns for investment casting, reducing or eliminating engineering changes in production, and providing small production runs.
In some of these applications, such as the verification of CAD design and testing of part functionality, the formation of a colorful object may not be considered as essential. In other applications such as aesthetics assessment, however, it may be desirable to have different colors on different parts of an object. Automated SFF systems that are currently available for building three dimensional parts do not provide color manipulating capabilities.
As an example, one commercially available system, stereo lithography (SLy), employs software to slice a computer generated solid model, represented by CAD data, into thin cross sections. The cross sections are then physically created by scanning a spot of ultraviolet laser light over a top surface of a reservoir of photo-curable liquid polymer. The laser beam partially cures the photo-curable material at the scanned spots, changing the material from a liquid to a solid. After forming a given layer an object-supporting platform is lowered within the reservoir by an amount equal to the thickness of the layer created. The scanning process is repeated for the next layer, followed by platform-lowering. These procedures are repeated until all the constituent layers of the object are formed. After fabrication subsequent steps are typically required to drain the unused resin and to fully cure all of the photopolymer that may be trapped within the partially cured material. The SLy systems make use of expensive photo curable polymers to make objects that normally contain difficult-to-clean uncured resin residue. They do not provide the capability for the operator to vary the color of the object.
The following three U.S. patents all teach aspects of 3-D object-building systems based on photo-curable polymers: U.S. Pat. No. 4,563,330, issued Mar. 11, 1986 to Hull, entitled "Apparatus for Production of Three-Dimensional Objects by Stereo lithography"; U.S. Pat. No. 4,752,498, issued Jun. 21, 1988 to Fudium, entitled "Method and Apparatus for Photo solidification"; and U.S. Pat. No. 4,801,477, issued Jan. 31, 1989 to Fudium, entitled "Method and Apparatus for Production of Three-Dimensional Objects by Photo solidification".
In another type of commercially available system, selective laser sintering (SLS), a thin layer of heat-fusible powder is spread over a surface by a counter rotating cylinder. A laser is employed to scan the powder layer, while its beam is modulated to melt the powder only in areas defined by the geometry of the cross section. A new layer of powder is then spread and melted, and the process is continually repeated until the part is completed. In general, the sintering systems are relatively expensive and require a significant amount of time to generate a finished part of average complexity from the input CAD data. Furthermore, the current SLS systems are not capable of generating an object with different colors at different locations of the object.
In a series of U.S. patents (U.S. Pat. No. 5,204,055, April 1993, U.S. Pat. No. 5,340,656, August 1994, U.S. Pat. No. 5,387,380, February 1995, and U.S. Pat. No. 5,490,882, February 1996), Sachs, et al. disclose a 3-D printing technique that involves using an inkjet to spray a computer-defined pattern of liquid binder onto a layer of powder. Another layer of powder is spread over the preceding one, and the process is repeated. The "green" part is separated from the loose powder when the process is completed. This procedure is followed by powder removal and metal melt impregnation or sintering. In another series of U.S. patents (U.S. Pat. No. 4,752,352, June 1998, U.S. Pat. No. 5,354,414, October 1994, U.S. Pat. No. 5,637,175, June 1997), Feygin report a technique called laminated object manufacturing (LOM). In this technique, a material delivered in a thin sheet form, coated with thermally activated adhesive, is glued to the previous layer by use of a heated roller. A laser outlines a CAD-defined cross section onto the sheet and, in nonsolid (unwanted) areas of the layer, it scribes a cross-hatch pattern of small squares. As the procedures repeat, the cross-hatches build up into "tiles," which are broken off the solid block to yield a finished part. Both 3-D inkjet printing and LOM methods, in their present forms, do not permit adjustable-color fabrication of an object.
The following U.S. patents are related to computer-controlled fabrication of three dimensional objects. In U.S. Pat. No. 4,665,492, issued May 12, 1987, entitled "Computer Automated Manufacturing Process and System" Masters teaches part fabrication by spraying drops or particles, a process commonly referred to as Ballistic Particle Modeling (BPM). In a series of patents (U.S. Pat. No. 5,746,844, May 1998, U.S. Pat. No. 5,718,951, February 1998, U.S. Pat. No. 5,669,433, September 1997, and U.S. Pat. No. 5,617,911, April 1997), Sterett, et al. disclose a method and apparatus for building metal objects by supplying, aligning and depositing nearly uniform metal melt droplets. In U.S. Pat. No. 5,398,193, issued Mar. 14, 1995, entitled "Method of 3-D Rapid Prototyping Through Controlled Layerwise Deposition/Extraction and Apparatus Therefor," de Angelis teaches a method that involves combined material additive and material subtractive procedures to build every constituent layer of an object. Andre teaches a method of incremental object fabrication in two U.S. Pat. No. 5,435,902, July 1995 and U.S. Pat. No. 5,614,075, March 1997. Brown discloses a method and apparatus for metal solid preform fabrication utilizing partially solidified metal slurry (U.S. Pat. No. 5,622,216, April 1997). Rock and Gilman reveal a method of producing a solid object using two distinct classes of materials, one material to form the object while the other material to form a complementary-shaped support that is later removed (U.S. Pat. No. 5,555,481, September 1996). In U.S. Pat. No. 5,578,227, November 1996, Rabinovich teaches a rapid prototyping system that involves drawing and positioning thin, continuous feedstock of materials which have various profiles with opposite flat sides and fusing the feedstock by welding a flat side with a laser beam to a flat side of a previous layer, while keeping the feedstock cross section in substantially original shape.
Another commercially available system, fused deposition modeling (FDM), employs a heated nozzle to extrude a melted material such as a nylon wire or a wax rod. The starting material is in the form of a rod or a filament, the latter being supplied from a spool. The filament is introduced into a flow passage of the nozzle and is driven to move like a piston inside this flow passage. The front end, near the nozzle tip, of this piston is heated to become melted; the rear end or solid portion of this piston pushes the melted portion forward to exit through the nozzle tip. The nozzle is translated under the control of a computer system in accordance with previously generated CAD data sliced into constituent layers. The FDM technique was first disclosed in U.S. Pat. No. 5,121,329 (1992), entitled "Apparatus and Method for Creating Three-Dimensional Objects," issued to S. S. Crump. The primary applications of this FDM technique have been the fabrication of prototypes and the creation of positive forms to be utilized in investment casting processes. The users of the FDM technology have heretofore been concerned primarily with the dimensional accuracy and surface finish of the final part. Little attention has been paid to the formation of a color pattern on the surface or inside the body of the final part.
A most recent patent (U.S. Pat. No. 5,738,817, April 1998, to Danforth, et al.) reveals a fused deposition process for forming 3-D solid objects from a mixture of a particulate composition dispersed in a binder. Fine ceramic and metallic powders were employed as the primary particulate component for making ceramic and metal parts, respectively. The binder is later burned off with the remaining particulate composition densified by re-impregnation or high-temperature sintering. This patent emphasizes the mechanical integrity of a part and again has paid little attention to the color form of a part. Batchelder, et al. (U.S. Pat. No. 5,402,351, 1995 and U.S. Pat. No. 5,303,141, 1994) reveal a model generation system having closed-loop extrusion nozzle positioning. These melt extrusion based deposition systems provide only a fixed-composition feed and do not lend themselves to varying the color of an object.
Therefore, an object of the invention is to provide a layer manufacturing process and apparatus for producing a colorful 3-D object.
It is a specific object of the invention to provide a process and apparatus for producing a multi-color object from a computer-aided design image of the object.
It is a further object of the invention to provide a computer-controlled object fabrication process and apparatus with which the color pattern of an object can be varied during the object-building process.
It is still another object of the invention to provide methods and apparatus for generating a CAD-defined object in which the color pattern can be predetermined.